A typical heavy-duty electrical generator design such as would be used on an industrial engine as the prime mover for construction equipment or the like generally includes a significant amount of iron and copper in the core and windings thereof. This concentration of material generates a significant amount of heat in operation and requires cooling to perform efficiently. Typically, a steel or aluminum fabricated, cast gray iron or aluminum cast annular exhaust fan is secured to the coupling between the engine flywheel and the generator drive shaft, and includes a plurality of paddle blades which push air through the generator windings and core to cool them as the flywheel and drive shaft rotate. Because of the significant forces created in the engine, a flexible connection of some sort is generally used to minimize the transmission of vibration and other such disruptive forces between it and the generator. Also because of these vibrational forces, and the significant torsional forces experienced not only from the overall speed of the engine, but also the torsional vibration of the engine experienced during normal operation, it has generally been thought that a very high strength metal must be utilized to ensure a long and reliable operational life for these exhaust fans which may typically be 24 inches in diameter. Of course, with fabricated and cast metal fans, balancing the fan is a critical step which must be attended to to ensure proper operation. Furthermore, if one of the fan blades would break, the entire fan would be out of balance and would have to be replaced, even though a significant portion of the fan remained intact. Of course, with diameters approaching 24 inches, or even larger, shipment of a replacement fan is not an easy task and generally requires that the fan be mounted to a wooden pallet or the like to prevent its breakage and to properly support it during shipping and before installation.
To solve these and other problems of the prior art, and to significantly reduce the cost of the fan and its repair, the inventor herein has succeeded in designing and developing a multi-part molded plastic fan for use in place of the one-piece metal cast fan of the prior art. The present invention consists of a 90.degree. annular segment which is plastic molded with two metallic sleeve inserts for mounting of the segment to the flywheel of the engine. At either end of each segment is an interlocking structure which takes a different form in each of two embodiments. In a first embodiment, one end is a flange-like member with a hole formed therein and the other end is a platform member with one of the metallic sleeves molded therein such that a flange of one segment overlies a platform of an adjacent segment with the hole in the flange fitting over the upstanding portion of the metallic sleeve, the sleeve extending substantially the entire height of the base of the segment. A bolt is then passed through the hole in the flange and the metallic sleeve and has a threaded end which secures the flange, the platform, and the flex plate coupling to the flywheel. With this interlocking structure, a bolt is used to secure each fan segment at its point of juncture to the flywheel. This is important as the fans are generally tested at greater than their normal operating speed for several hours at maximum operating temperature to ensure their long life in the field. This interlocking structure has been found sufficient to pass this test.
In another embodiment, the inventor has modified the interlocking structure by utilizing a half-height base member at one end of the segment, and a half-height base member at the other end of the segment, the half-height base members being arranged so that they overlie one another, with the same metal cylindrical sleeve being molded into one of the half-height base members and the other having a hole therein so that it may be fitted over the sleeve and mounted by a single bolt to the flywheel as with the first embodiment. This second embodiment is thought to be an improvement over the first embodiment in that it eliminates the somewhat thinner flange portion of the interlock and instead utilizes half-height base members which are thought to be less susceptible to cracking during operation.
With either embodiment, the interlocking structure at each end of each segment may be utilized to pre-assemble the fan prior to its assembly to the generator. In this regard, the metal cylindrical sleeves which are molded into the segments may be used to match and line up the segments and facilitate its pre-assembly prior to installation. Alternately, the fan segments may be individually mounted one at a time to the generator. This approach has the advantage of permitting the installer to handle smaller pieces of the fan and support it as it is being installed. Although it is generally believed that pre-assembly of the segments into a fan results in easier installation in the majority of designs, either approach may be utilized depending upon the particular design and preference of the installer.
The inventor has found that 20% to 40% glass-filled nylon plastic is suitable for use in molding the segments used to form the multi-piece annular fan of his invention. Alternately, carbon fiber filled plastic may be used to give greater strength. If made from carbon filled plastic, it is believed that the metal cylindrical sleeves may be eliminated. Other plastics exhibiting similar characteristics could be utilized as well. As mentioned above the use of plastic significantly reduces the cost of the fan for several reasons. These include the basic material cost used to initially manufacture the fan, the elimination of the balancing and machining steps, the significant reduction in the tooling cost due to the smaller piece size, and the significant savings not only in shipping the smaller plastic segments, but also the reduction in repair costs made possible by the ability to replace only that portion of the annular fan which has failed.
The foregoing has been a brief summary of some of the principal advantages and features of the invention. A more detailed understanding of the invention may be obtained by referring to the drawings and description of the preferred embodiment which follow.